The prior art includes the following:                (1) The tunable impedance surface, invented at HRL Laboratories of Malibu, Calif. See, for example, the following U.S. Pat. Nos.: 6,483,480; Sievenpiper, and Sievenpiper, U.S. Pat. No. 6,538,621. The tunable impedance surface is described in various incarnations, including electrically and mechanically tunable versions. However, the tuning technology disclosed herein is different in that relates to a tuning method that allows for the independent control of the phase preferably at each element of the tunable impedance surface.        (2) Phased array antennas. These are described in numerous patents and publications, and references. See, for example, U.S. patents by Tang, U.S. Pat. No. 4,045,800; Fletcher, U.S. Pat. No. 4,119,972; Jacomini, U.S. Pat. No. 4,217,587; Steudel, U.S. Pat. No. 4,124,852; and Hines, U.S. Pat. No. 4,123,759. Phased array antennas are typically built as arrays of independent receiving elements, each with a phase shifter. Signals are collected from each element and combined with the appropriate phase to form a beam or null in the desired direction. The disadvantage of the phased array compared to the present technology is that it is prohibitively expensive for many applications.        (3) Adaptive antennas. These are also described in numerous patents and publications, and references. See, for example, U.S. Patents by Daniel, U.S. Pat. No. 4,236,158; Marchand, U.S. Pat. No. 4,220,954; McGuffin, U.S. Pat. No. 4,127,586; Malm, 4,189,733; and Bakhru, U.S. Pat. No. 4,173,759. Adaptive antennas include analog or digital signal processing techniques that are used for angle of arrival estimation, adaptive beam forming, adaptive null forming, including the ability to track multiple sources or jammers. The disadvantage of traditional adaptive antenna methods compared to the present disclosure is the required complexity. Many of the same functions that are used in traditional adaptive antennas are handled by the presently disclosed technology using much simpler techniques.        (4) The prior art also includes the ESPAR antenna system developed by Ohria, U.S. Pat. No. 6,407,719. This antenna involves a series of passive antenna elements and a single driven antenna element. The resonance frequencies of the passive antenna elements are adjusted to vary the coupling coefficients among them, and to steer a beam or a null. The presently disclosed technology is related to this antenna in that it preferably uses passive, non-driven resonators as the beam forming apparatus. However, the presently disclosed antenna technology allows much higher gain because it allows the radiation striking a large area to be directed to a single feed, rather than relying exclusively on mutual coupling among the elements.        
The technology disclosed herein improves upon the existing state of the art in that it provides a lower cost alternative to traditional phased arrays, while retaining the same functionality, including the ability to adaptively modify the phase profile by measuring a small number of parameters. Phased arrays are typically expensive, often costing hundreds of thousands or millions of dollars per square meter for an array operating at several GHz. The technology disclosed herein utilizes a tunable impedance surfaces, a concept that has been described in the U.S. Patents referred to above, but the presently disclosed technology provides the ability to adaptively modify the reflection phase to optimize a variety of parameters. If the number of measured variables is limited, then this method further reduces the cost compared to conventional techniques. Calculations that ordinarily require complex digital signal processing are handled naturally by the adaptive array without difficult data processing requirements.
The technology disclosed herein can be used in a variety of applications. For example, it can be used for a low-cost communication system. It can also be used for a low-cost in-flight Internet system on aircraft, where data would be directed to passengers or users in various parts of an aircraft. Since the technology disclosed herein is blind to the incoming phase profile, it is able to partially mitigate multipath problems. It can also be used as a low-cost beamforming technique for information kiosk applications or for 3G wireless networking, in order to provide much greater performance in a vehicle, for example, than is possible with handsets.
An advantage of the present technology compared to a conventional phased array, besides the fact that this technology is comparatively inexpensive to implement, is that conventional phased arrays typically involve explicit control of the phase of a lattice of antennas, while in the antenna systems disclosed herein, the phase at each point on the surface is an intermediate state that exists, but has no direct bearing on the control of the array. In other words, the user does not need to calibrate the array to know its phase, because the antenna can be steered using the method disclosed herein without explicit knowledge of the phase. Conventional phased arrays, on the other hand, typically require explicit knowledge of the phase at each point in the array.